The present invention generally relates to wireless communication systems and particularly relates to determining a present location of a wireless mobile terminal.
Wireless technology progresses continuously, with newer technologies providing increased user capacity, improved quality of service, and new user convenience features. With enhanced data services, many newer mobile terminals allow users to send and receive email, as well as browse the World Wide Web. Some newer convenience features depend on the ability to determine a mobile terminal""s physical location. For example, the ability to determine mobile terminal location has commercial value with regard to targeted or location-sensitive advertising. However, the need to accurately determine the present physical location of a given mobile terminal extends beyond considerations of commerce and convenience.
In emergency situations, the ability to quickly determine a mobile terminal user""s physical location can be a matter of life-and-death. Knowing where one is at precisely enough to provide meaningful directions is challenge enough, even absent the duress of an emergency situation. For emergency services personnel to receive reliable location information, location data must come from the wireless communication system, the mobile terminal itself, or some combination thereof. In the United States, these concerns over the need to quickly locate mobile terminal users in emergency situations have sparked legislation imposing requirements on wireless service providers to field wireless communication systems that provide mobile terminal locating capabilities.
While several techniques exist for determining mobile terminal location, including approaches based on radio signal time-of-arrival between a given mobile terminal and multiple base stations, techniques based on the Global Positioning System (GPS) offer perhaps the most straightforward approach for reliably determining positions to within 100 meters or less. Consequently, an increasing number of mobile terminals include GPS functionality, enabling theses terminals to use GPS satellite signals to determine their current geographic location with relatively high precision.
A GPS-equipped mobile terminal may operate similar to recently popularized hand-held navigation units that provide current geographic location based on processing GPS satellite signals. That is, a GPS-equipped mobile terminal uses precise information about GPS satellite positions and GPS system time to derive its current geographic position. To determine position accurately requires detailed information about the orbits and positions of the GPS satellites. Because of the low communication bandwidth of the GPS signal, initially receiving and subsequently updating this GPS data from the GPS satellites is a lengthy process. While such delays are tolerable in conventional GPS navigation units, such delays are not acceptable in the context of emergency calling from a mobile terminal.
The present invention provides a system and method to reduce the time required for determining a mobile terminal""s geographic position in, for example, emergencycalling situations. To reduce the time required for determining the mobile terminal""s position at the outset of a call, the mobile terminal maintains stored position assistance data, such as GPS data, that expedites GPS satellite signal acquisition and processing. In an analog service area, the mobile terminal may periodically update stored GPS data using information received from available GPS satellites. In a digital service area, the mobile terminal typically preferably receives the supporting GPS data from the supporting wireless communication network rather than from the GPS satellites. If the mobile terminal obtains GPS data while operating in a digital service area, it can later use this data in an analog service area to expedite position determination, provided the data has not aged too much to be useful.
The position assistance data stored in the mobile terminal typically includes GPS almanac, ephemeris, clock and ionosphere corrections, and timing and location references. Wireless communication networks based on digital communication standards, such as TIA/EIA-136, IS-95, and GSM, include provisions for transmitting data, which may include position assistance data, to mobile terminals during standby conditions. However, analog standards, such as AMPS, typically do not include this capability,. Additionally, the bandwidth available on analog channels, both voice and control, is low as compared to the digital communication standards. In many areas it is likely that the operator of the wireless communication system will not deploy the provision of GPS assistance data on analog channels.
To fully exploit opportunities for using position assistance data already stored in the mobile terminal for position determination in analog service areas, GPS data should be periodically refreshed via the supporting wireless communication network while the mobile terminal operates within a digital service area. Alternatively, either the mobile terminal or the wireless network can predict when a move into an analog service area is likely, and update needed portions of the GPS data in response. In this manner, if the mobile terminal subsequently moves into the analog service area, it does so with substantially current GPS data. The advantage of this is faster acquisition of the satellite signals and computation of a position, thereby reducing the power consumption and improving the quality of service provided by the mobile terminal.